In recent years, a railroad car equipped with a battery unit such as a secondary battery has begun to attract notice for reducing an environmental load. For example, a hybrid driving system, where a diesel engine is as power of an electric generator and the electric power is stored in a secondary battery while a motor is driven using electric power generated by the electric generator and the power of the secondary battery is used at a start or at acceleration etc., has been proposed. The secondary battery of the foregoing hybrid driving system can store not only the generated electric power, but also the electric power generated by a regenerative brake.
As the secondary battery for a rail car, a nickel hydride battery or a lithium-ion battery is often used. In these secondary batteries, an excess charge/discharge is a cause of deterioration. For this reason, it is proposed that a charge control system such as that if the secondary battery charges more than a predetermined first threshold by measuring an remained amount of the electric power stored in the secondary battery, then the charge is not executed moreover, adversely, if the remained amount is less than a second threshold, which is different from the first threshold and less than the first threshold, then the discharge is not executed moreover.
Further, it is proposed that such a control system is as that when discharge current exceeds the permissible current for the secondary battery, then output is limited, and adversely, when the charge current exceeds the permissible current for the secondary battery, changing to the other braking method such as a generative brake, a regenerative electric power charge is evaded.
As just described, in a system using the secondary battery, various proposals for restraining an excess charge/discharge are considered. In addition, a proposal such as that the secondary battery is provided with disperse in a train set which is constituted by a plurality of rail cars in which power sources are dispersed, is conventionally considered. According to the proposal, the charge/discharge of the secondary batteries can be controlled. The above mentioned technology is disclosed in Japanese Patent Application Publication No. 2011-61880, and contents of which are hereby incorporated by reference. Further, the above mentioned technology is disclosed in JR EAST Technical Review No. 34 pages 23-32, and contents of which are hereby incorporated by reference.